Panels for floating covers, floating covers and methods for making them

ABSTRACT

A floating cover ( 12 ) for a liquid storage tank ( 10 ) is made from a plurality of prefabricated sandwich panels ( 30 ). Each panel has an upper glass fibre composite layered portion ( 34 ), a honeycomb layer ( 36 ) the same size as the upper composite layered portion ( 34 ), and a lower fibre glass composite layered portion ( 32 ) that extends around the edges of the honeycomb layer by about 0.1 m. The panels are laid adjacent and abutting each other on a supporting form work, and the gaps above the extended lower layered portion ( 32 ) are filled in with sandwich sections similar to the structural layers of the sandwich panels. The upper parts of the in-fill sections overlap the upper layered portions ( 34 ) of the prefabricated panels by about 0.1 m.

FIELD OF THE INVENTION

This invention relates to panels for floating covers, floating coversand methods of forming them, particularly for use in large liquidstorage tanks, for example for preventing contamination to/from thecontent of the tanks and evaporation losses. More specifically itrelates to such covers being made from prefabricated sandwich panels.

BACKGROUND OF THE INVENTION

Storage tanks are in common use at storage terminals or processingplants where huge stockpiles of liquid raw materials are necessary fortheir continuous operations. These storage tanks usually employ floatingcovers that move as the liquid levels change, and these covers provideprotection against contamination to/from the external environment orweather and against evaporation losses.

The covers are typically made of steel or aluminium, mainly due to theirease of welding and their availability as construction materials.However, steel covers corrode relatively easily and are costly tomaintain. For aluminium covers, the initial capital outlay is high butthe maintenance cost is lower than that of steel. The materials of thesecovers or their coatings must also be compatible with the content in thetanks.

These tanks are usually very large and may range from a few metres toabout a hundred metres in diameter. Before construction begins, aplatform supported on scaffolding is erected and the cover is thenformed on the platform. Due to the size of the cover, this type ofconstruction is invariably carried on site. Owing to the nature of work,it involves welding from both sides, and this requires welders to carryout overhead welding from below the platform. However, welding createshazardous fumes, and the working space, especially that below theplatform must be properly ventilated.

It has also been known to make such covers from sheets of glass fibre,which overlap at their edges and which are supported on their undersidesby buoyant urethane foam frames, for instance as is disclosed inpublished patent document GB 983,797. This too involves constructionfrom both sides and in almost 40 years since publication has not reallycaught on.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided agenerally planar buoyant panel for a floating cover for a liquid storagetank, the panel comprising first and second portions in contact witheach other, and wherein:

the first portion has an extent in the plane of the panel and a firstside facing the second portion;

the second portion has an extent in the plane of the panel, which extentis less than the extent of the first portion; and

the first portion has an exposed portion on said first side.

According to a second aspect of the invention, there is provided aplurality of panels, as above, wherein the first portion of each panelhas an edge generally orthogonal to the plane of the panel, and theedges of the first portions of adjacent panels abut each other.

According to a third aspect of this invention, there is provided abuoyant cover for a liquid storage tank comprising a plurality of panelsas above.

According to a fourth aspect of this invention, there is provided amethod of joining a plurality of generally planar buoyant panelstogether, for use in forming a floating cover, wherein each panelcomprises first and second portions in contact with each other, with thefirst portion of each panel having an extent in the plane of the paneland a first side facing the second portion, the second portion of eachpanel having an extent in the plane of the panel, which extent is lessthan the extent of the first portion; and the first portion having anexposed portion on said first side (or the panels may be as above), andwherein the plurality of panels are placed together, with adjacentpanels abutting each other, the edges of the first portions of adjacentpanels which are orthogonal to the planes of the panels being incontact, the method comprising the step of:

inserting infill portions between adjacent panels, the infill portionsextending in contact with the exposed portions of adjacent and abuttingpanels.

This may be used to produce a buoyant cover as above and/or may be amethod of forming a floating cover.

According to a fifth aspect of this invention, there is provided amethod of constructing a floating cover for a liquid tank from aplurality of panels, wherein the panels are securely joined together bypeople working on just one side of the cover.

According to a sixth aspect of this invention, there is provided amethod of constructing a floating cover for a liquid tank from aplurality of panels, comprising the steps of:

placing said plurality of panels on a form work;

joining said panels together; and

removing said form work;

wherein the joining step prior to the removing step is accomplishedsolely from one side of the cover.

According to a seventh aspect of this invention, there is provided amethod of testing the integrity of joints in a floating cover formed bya plurality of panels, as above, comprising the steps of:

providing at least one testing port in said infill portion at a boundarybetween said infill portion and a panel second portion;

applying a pressure differential between the testing port or one of thetesting ports and the outside of the cover;

determining if there is a leak between the one testing port or said oneof the testing ports and the outside of the cover; and

if there is a leak, identifying the leak.

Preferably, a pump delivers air or nitrogen to the test port at apredetermined pressure. A liquid, such as a soap solution, may be usedfor detecting leaks from any defective portion of the cover.

A plurality of drain holes may be provided at the lower surface of thefloating cover of one or more of the above aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described by way of non-limitative examples,with reference to the accompanying drawings, in which:—

FIG. 1 is a cross-section illustrating a typical liquid storage tankusing a floating cover of the type described in this invention;

FIG. 2 illustrates cross sectional details of a sandwich panel making upthe floating cover according to an embodiment of this invention;

FIG. 3 illustrates cross sectional details where two prefabricatedsandwich panels join together; and

FIG. 4 is an exploded view of the component parts of FIG. 3.

FIG. 5 illustrates a portion of the floating cover with a test port fortesting if the sandwich panel joints are airtight.

FIG. 6 illustrates a portion of the floating cover with another testport and a drain port.

DETAILED DESCRIPTION

FIG. 1 illustrates a large storage tank 10 having a cover 12 floating onliquid 14 contained in the tank. This floating cover 12 is made up of anumber of prefabricated sandwich panels joined together.

The cover 12 includes other components for operation of the storagetank. For example, a ring flange, with a cross-sectional shape of aninverted “L” is provided around the peripheral edge of the cover. Aflexible metal seal 16 is mounted on this flange to co-operate with theinternal wall of the tank to keep the content of the tank beneath thecover 12 and to prevent external contaminants from entering. A pluralityof vents is equally spaced along the ring flange is to allow forexpansion or contraction of vapour that may be present in the tank asits temperature varies during the day. Other types of vents may also beprovided, for example a vacuum breaker vent to allow the liquid in thetanks to be emptied, when the cover is resting on the tank floor and isno longer floating. This is to prevent damage to the cover caused bynegative pressure when the balance of the content is pumped out.

Draining or sampling points are arranged in order to allow samples ofthe contents of a tank to be taken. Further, a gauge pole well is alsoprovided for determining the quantity of the content in the tank.

Fittings, such as a wire rope 18 fixed between the roof and floor of thetank and passing through the cover prevent the cover 12 from rotating.

Vertically extending legs 20 are spaced apart below the cover 12 atregular intervals. These legs are provided to support the cover 12 whenthe scaffolding has been removed after the cover is completed and beforethe tank 10 is filled with sufficient liquid for the cover 12 to float.The legs 20 also provide headroom below the cover 12 for maintenancepurposes. A hatch-cover complete with seals over a man-hole is alsoprovided for maintenance purposes.

These provisions for the operation of the tank, such as the vents,sampling and drain points, anti-rotation fittings, legs or man-holehatch cover, etc mean that some of the panels have apertures or flangesto allow them to be fitted, or are formed with various componentsalready installed.

A roof 22 covers the whole tank 10.

A prefabricated sandwich panel 30, used to make up the floating cover12, is shown in cross-section in FIG. 2. Because each panel is very muchthinner than it is long or wide, the relative depth and width isdistorted in FIG. 2 and other figures. Likewise, there is a distortionin the relative thicknesses of the different layers.

Each panel 30 has a lower glass-fibre reinforced composite layeredportion 32, an upper glass-fibre reinforced composite layered portion 34and a honeycomb section (portion) 36, to provide buoyancy, sandwichedbetween the lower and upper layered portions 32,34. Each portion ispreferably continuous, in that there are no holes or gaps all the waythrough them. The panels are joined together, with the lower layeredportions 32, edge 38 to edge 38, to form the entire floating cover 12.

Both the lower layered portion 32 and the upper layered portion 34 arethemselves composite, laminar structures of several layers, each ofwhich contains a liquid polymerise resin such as an epoxy resin, forinstance epoxy vinyl ester resin, and glass fibres. The glass fibres areorientated in different patterns or directions, at least relative toimmediately adjacent layers to provide each panel with required strengthand other desired mechanical properties.

In general composition, in this exemplary embodiment, the lower andupper layered portions 32,34 are mirror images of each other, althoughextending different amounts in the plane of each panel 30.

In the lower layered portion 32, the lowermost (outer) layer 42, is aV-layer. Above the V-layer 42 is a first mat or M-layer 44. An R-layer46 is disposed above the first M-layer 44. A second M-layer 48, of asimilar composition to the first M-layer 44 is provided on top ofR-layer 46. This is the topmost layer of the lower layered portion 32and is adjacent the underside of the honeycomb section 36.

The upper layered portion 34 is the inverse of the lower layered portion32, with a V-layer 52 uppermost, above a first M-layer 54, above aR-layer 56 above a second M-layer 58, which is adjacent the topside ofthe honeycomb section 36. The V-layer 52, first M-layer 54, R-layer 56and second M-layer 58 of the upper layered portion 34 have the samegeneral composition as their corresponding layers in the lower layeredportion 32.

The V-layers (surface veil layers) 42, 52 have a surfacing veil glassfibre mat of C glass reinforcements and have carbon (and colour pigmentsif desired) and enhance the surface finish as well as providing weatherprotection and corrosion resistant properties. Typically they are about90-95% by weight of resin and about 0.5-0.6 mm thick. Different V-layerswithin the same panel can be of differing construction.

The M-layers (mat layers) 44, 48, 54, 58 have a chopped strand mat ofglass fibres that are of certain lengths but are randomly orientated.Typically they are about 60-70% by weight of resin and about 1.1-1.2 mmthick. The M-layers absorb relatively more resin and give relativelyhigher resistance to corrosion to the composite layered portions 32, 34.Different M-layers within the same panel can be of differingconstruction.

The R-layers (woven roving layers) 46, 56 have a woven roving mat ofglass reinforcements that are woven in two perpendicular directions.Typically they are about 40-50% by weight of resin and about 1.1-1.2 mmthick. Due to the orientations of the reinforcement, the R-layersprovide mechanical strength in two directions. The lower resinabsorption of these layers increases the glass to resin ratio withconsequent increased mechanical strength. Different R-layers within thesame panel can be of differing construction.

The honeycomb layer 36 is made of a polypropylene core, with twomembranes on each side. An inner membrane permanently attaches to thecore and acts as a seal to prevent resin penetration into the cells ofthe core. An outer membrane of a non-woven thermoplastic mat is porousand allows the resin of the composite layered portions (when wet) topenetrate and bond to the membrane's surface. The resulting bondcontributes to the overall structural integrity of each panel 30.

This honeycomb layer 36 and its core may be substituted with other typesof lightweight core materials as desired or appropriate.

The panels 30 are prefabricated at a factory. Each panel is typically2.2 m square, this size being selected on a weight of about 70-80 kg perpanel and general cumbersomeness. Each panel is not too heavy or largefor a group of four to manhandle. As most storage tanks are cylindrical,a cover for such a tank would also be circular. This means that not allpanels will be square, but some will have a rounded edge according tothe overall radius of the tank.

Generally the composite is made in a large continuous and uniform sheetwhich is cut into appropriately sized panels 30. Portions of each panelare then removed around its edges to give it a stepped form, as is shownin FIG. 2. In particular, the upper layered portion 34 and honeycombsection 36 are removed from a strip around every edge, in this examplethe strip is 0.1 m wide. Thus the lower layered portion 32 extends 0.1 mbeyond the upper layered portion 34 and honeycomb section 36 in anexposed portion 50 in each direction in the plane of the panel 30.Further, the top V-layer 52 is stripped back a bit further at its edges,leaving an exposed strip 40 of the top first M-layer 54. Again thisstrip is 0.1 m wide in this example.

Of course the panels do not have to be formed in this way, the steppedform can be achieved in the original fabrication stage or in other ways.

Before installation of the cover 12, form work scaffolding is erectedand a platform is provided so that the panels 30 making up the entirecover 12 can be laid out with contiguous contact between the edges ofthe lower layered portions 32. In the spaces above the extended edges ofthe lower layered portions 32, the upper, horizontal surfaces areroughened with sandpaper, emery cloth or similar abrasive (for examplehaving a grade size of about 30), if this has not been already beendone. The resulting dust is removed by vacuum cleaning, otherwise theresidue may cause weak bonding and joint failure.

A joint between adjacent panels 30 is shown in FIG. 3. An exploded viewof this is shown in FIG. 4.

The resin used in the V-layer is then applied to the extended facingedges 38 of the lower layered portions 32. However, rather than justfilling in the gap between adjacent honeycomb structures 36 with morehoneycomb, a reinforcing structure is mounted over the joints betweenadjacent panels 30. In particular, the gap is filled with what amountsto a narrower inverted panel with the top V-layer 52 completely removed.That is there is a reinforcing infill composite 60, having a firstM-layer 62 in contact with the abutting second M-layers 48 of twoabutting lower layer portions 32. Above this is a first R-layer 64, thena second M-layer 66. Atop this is a honeycomb structure 68, on top ofwhich is a third M-layer 70, then a second R-layer 72, then a fourthM-layer 74 and finally a topmost V-layer 76.

Whilst it is possible to prefabricate the infill composite 60 in panels,for improved strength it is preferred that they be made in situ. Inparticular, a catalysed resin is applied to the exposed and roughenedsurfaces 50 of the second M-layers 48 and the infill composite isapplied one layer at a time, either with each layer prefabricated ormore preferably each layer made in situ, with some of the resin seepingdown between the abutting edges 50 of the panels to help join themtogether. After each layer is laid down, it is compacted and air bubblesthat may be present are rolled out, for example using metal rollers.

Before the resin bonding the infill second M-layer 66 to the infillfirst R-layer 64 in this lower structural infill portion 78 has hardenedor cured, a catalysed resin is applied to the underside of the infillhoneycomb structure 68 and this is applied to the top of the infillsecond M-layer 66. It is held down by weights until it has completelycured. An infill top structural infill portion 80, with the remaininglayers, is then applied to the top of the infill honeycomb structure 68.Again this is done on a layer by layer basis, compressing the layers androlling out the air bubbles each time. This completes the joint. Onceall the cover joints have been completed, the top surface can befinished off with any required top coat.

The creation of the infill composite 60 reflects the creation of theinitial composite from which the panels are formed. Thus if there areadditional or fewer processes in creating that, they could be reflectedin the creation of the infill. This means that the infill has similarproperties to the panels. Additionally it means that the heights ofvarious layers of the infill correspond to heights of other layers inthe panels. In particular, the top of the infill honeycomb structure 68is level with the top of the exposed top first M-layer 54 and the infillthird M-layer 70 is level with the top V-layer 52.

Further, the top infill structural portion 80, that is the third M-layer70, second R-layer 72, fourth M-layer 74 and topmost V-layer 76, extendfurther outwards relative to the rest of the infill structure 60. It isabout 0.4 m wide, whilst the infill honeycomb structure 68 and lowerstructural infill portion are about 0.2 m, or a little less wide (toallow resin between the panels 30 and the infill composite 60. Thismeans that the top infill structural portion 80 extends as far as theexposed top first M-layer 54, the infill third M-layer 70 bonding to thetop exposed surface 40 of the top first M-layer 54. The top V-layer 76may also be extended down the exposed sides of the top structural infillportion 80, to join up with the top V-layers 52 of the panels beingjoined, to complete the outer protective layer.

After completion of the cover, the form work is removed from theunderside and exposed edges on the underside are sealed and laminatedwith a further V-layer. This is to improve corrosion resistance, ratherthan being necessary for strength.

The construction of the cover 12 from separate panels 30 by this methodcan be carried out from just one side, the top side, although thepreferred finishing step after completion is carried out below. This ispartly due to the fact that the panels are connected edge to edge, withvertical edges next to each other and without overlap. This means thatpeople do not have to work in cramped and badly ventilated conditionsunderneath, thereby improving safety. Breathing equipment is thereforenot necessary, or does not need to be used so much and there areimprovements in work conditions and costs.

With this method of construction, the prefabricated panels are joinedtogether to form an entire cover having similar structural layers. Thismethod provides a cover that is mainly prefabricated at the factory andminimal work is carried out on site. As the working conditions andquality at the factory is easily controlled, this means that thestructural integrity of the cover thus formed is relatively superior tothat if formed on site. With this method, the entire job for completinga cover is also shorter, which means cost savings.

The lower and upper layered portions 32,34 are formed layer by layer inthe factory to suit each application. The resins binding the fibres ineach layer may also differ from the adjacent layers, and together withthe glass-fibres, each layer provides the composite plate uniquemechanical properties. The composition and number of layers of panelscan vary from job to job, within the scope of the invention.

In this example, each lower and upper layered portion 32,34 is 4 mmthick and the honeycomb layer is 60 mm thick. Depending on the size ofthe cover, the core thickness, the spacing between the supporting legs,the self-weight of the cover, the strength of the resin and glassfibres, the rigidity of the cover, the composite plate thickness or thenumber of laminates may vary, all relative to each other. Similarly, thehoneycomb thickness or number of honeycomb layer may be increased forgreater strength or rigidity. Yet it is also possible to maintain acommon composite thickness and strength by providing more supportinglegs at the lower side of the cover.

The exposed portions in the described embodiment are 0.1 m wide. Theinvention covers other possibilities as required. For example, theycould range from 0.05 to 0.2 m or to other widths. The extension of thelower layered portion 32 relative to the upper layered portion 34 andcore 36, and the overlap of the top infill structural portion 80 neednot be 0.1 m but could be different from each other and can be varied asdesired, for instance depending on the type of resin used and the shearforces induced at these joints, etc. Moreover, the steps do not need tohave vertical faces, but can be sloped.

The materials chosen for the cover need to be compatible with the liquidin the tank.

The completed floating cover 12 may need to be inspected and tested toverify that the floating cover 12 formed according to the specificationof work meets the industry or regulatory standards during and aftercommissioning. To allow testing that the bonding of the layers of thefibreglass and resin and joints are integral, testing ports 90 may beprovided at the infill composite section 60 near the cut edges of thehoneycomb 36, 68 as shown in FIG. 5.

The infill honeycomb sections 68 are generally slightly smaller than thespace between two adjacent honeycomb sections 36. This is to allow fordimensional tolerances in the fabrication of the panels 30 and honeycombsections 68. As a result there is a gap 92 in between the cut edges ofthe honeycomb sections 36, 68, and this gap 92 runs along the fabricatedjoints between the panels 30. In an integrally constructed floatingcover 12, the gap 92 is sealed by the lower composite layers 32, 78,upper composite layers 34, 80 and honeycomb sections 36, 68.

To provide a testing port 90, a hole 94 is drilled through the uppercomposite layer 80 to the cut edge of the honeycomb 68. Epoxy resin suchas that mixed with the catalyst used in fabricating the panels 30 isapplied onto the walls of the hole 94. A sleeve 96, preselected to suitthe hole 94, is inserted into the hole 94, and the gap, if any, betweenthe hole 94 and the sleeve 96 is further filled with epoxy and catalystso that there is no void between the hole 94 and the sleeve 96. Thebonding between the composite layer 80 and the sleeve 96 can thereby beas strong as the composite layer 80 itself.

The sleeve 96 has a through hole with an internal thread. In the processof inserting the sleeve 96 in the hole 94, precautions are taken not toallow the epoxy to block the internal hole of the sleeve 96. The upperend of the sleeve 96 may be temporary closed with a plug 98 (which mayextend all the way to the bottom of the sleeve 96).

A number of test ports 90, for example, are provided at spaced apartpositions. One such port 90 should normally be sufficient, as the gaps92 are all joined together. However, more than one is provided to givethe tester a choice of testing positions or in case some groups of thegaps are isolated. After the sleeves 96 are bonded to the compositelayer 80, all the test ports except one are plugged. A nipple 100 isattached to the test port 90 which is not plugged. The nipple 100 isscrewed into the internal thread of the sleeve 96 so as to form anairtight joint. A first end of a T-joint 102 is connected to the otherend of the nipple 100. The other two distal ends of the T-joint 102 areconnected to a pressure gauge 104 and a shutoff valve 106. The shutoffvalve 106 has a thread that is suitable for connection to a line from apump 200.

During commissioning of the cover 12, the pump 200 is operated todeliver a gas, for example air or nitrogen, to the enclosed spacecreated by the gap 92 between the panels 30 in the floating cover 12.The gas is delivered with a positive pressure, for example 0.005 bargauge (or 50 mm water head), and the shutoff valve 106 is closed once apredetermined pressure is attained. The pressure in the enclosed spacein the floating cover 12 is monitored over a period of time, for example24 hours. If this pressure is maintained over this time period, thejoints formed in the panel are airtight. If the pressure is notmaintained, one or more joints is not airtight. The actual leakingjoints may be detected by applying a liquid such as a soap solution to aportion of the floating cover and observing air bubbles from a defectiveportion of the cover 12. The defective portion of the cover can then beidentified, repaired and tested again to ensure that the joints formedin the floating cover 12 are not defective.

To test for leaks in the joints, a vacuum pressure may be used insteadof a positive pressure. Accordingly, the pressure gauge must be suitablefor vacuum sensing. However, to identify the defective portion of thecover with ease, a positive pressure and a liquid such as a soapsolution are used.

When the floating cover 12 is put into use, these testing ports 90 areplugged up to prevent entry of vapour or liquid into the cover.

Although the hole 94 is smooth in the above embodiment, alternatively,the hole 94 may be threaded to fit an externally threaded sleeve.

Another alternative is to locate the sleeve 96 in the infill compositesection 60 as the infill composite section 60 is made.

A further alternative for the test ports is to provide the sleeve 96with a flange 300 having an internal hole through which the sleeve 96 ispositioned and to which the sleeve 96 is welded, to form a test port 91as shown in FIG. 6.

The flange 300 and sleeve 96 may both be made of metal, for example,steel or aluminium. The flange 300 is toroidal, for example with anoutside diameter of about 70 mm and a thickness from about 3 mm to about5 mm. Other shapes of the flange 300 are also suitable, althoughpreferably they can fit an inscribed circle within them, for example ofat least 70 mm diameter. The sleeve 96 has an internal thread and aninternal bore of 12-mm, for example, nominal diameter. In the preferredembodiment, the internal pressure is to be 0.005 bar gauge. Thus theexternal diameter of the sleeve may, for instance, be 25 mm. Thediameter of the flange through hole matches the external diameter of thesleeve 96. Thus if a different pressure rating were required, theexternal diameter of the sleeve 96 might change, and so would the sizeof the flange through hole. The sizes of the sleeve 96 and flange 300are not limited by these examples, and the sizes of the sleeve 96 andflange 300 are merely design choices.

The sleeve 96 and flange 300, which are prejoined together, are insertedduring the formation of the infill composite portion 60. After thestructural layers 70,72,74 of the infill composite portion 60 areformed, the hole 94 is drilled. Catalysed epoxy is applied to the wallsof the hole 94 and the sleeve 96 is inserted such that there is no voidbetween the hole 94 and sleeve 96, as done in the previous embodiment.Catalysed epoxy is also applied to the upper, lower and edge surfaces ofthe flange 300. With the test port 91 fully inserted, i.e. with thesleeve 96 portion pushed all the way down into the hole 94 until theflange 300 is in contact with the top M-layer 74, another set ofstructural fibreglass layers 70,72,74 is formed over and around theflange 300 to secure the test port 91 to the floating cover 12, and alsoto strengthen the structural layers of the cover 12 around the test port91. Once all the structural work is completed, the V-layer 76 is formedover the exposed layers of the infill portion 60 to complete thefinishing and protective layer 76.

In this embodiment as shown in FIG. 6, a plurality of drain ports 191are provided on the lower side of the floating cover 12. These drainports 191 are provided so that any liquid that has entered the cover 12,such as the liquid from the storage tank 10 (which entered duringmaintenance or repair of the floating cover 12 or otherwise) or rainwater collected on the uncompleted floating cover 12 during itsfabrication, can be drained out. Each drain port 191 is fabricated inthe same manner as a test port 91, i.e. having a flange 302 welded to asleeve 97.

After the floating cover 12 is formed and the supporting formwork isremoved, a plurality of positions directly below the gap 92 are markedon the lower surface of the cover 12. These positions are spaced apartas desired. At each position, a hole 95 is drilled through thestructural layers 42,44,46,48 of the cover 12. The V-layer 42 in thearea around each hole 95 is removed, if not previously done, over anarea extending beyond the size and shape of the flange 302. The flange302 is positioned on the sleeve 97 and they are prejoined together, suchthat when of the sleeve 99 is inserted into the hole 95 until the flange302 is in contact with the exposed area of the outer M-layer 44 and theupper end of the sleeve 97 is about flush with the inner M-layer 48.Catalysed epoxy is applied onto the exposed area of the outer M-layer44, onto the surfaces of the hole 95 and also on the upper, lower andedge surfaces of the flange 302. The sleeve 97 is then inserted into thehole 95 until the flange 302 is in contact with the exposed layer 44.Each drain port is mounted and secured onto the cover 12 by forming aset of structural layers of fibreglass 70,72,74 over and around theflange 300 of the drain port 191 similar to layers 70,72,74 over andaround the test port 91. Once the structural work is completed, aV-layer similar to layer 42 is formed over the exposed surfaces of thenewly laid structural layers 70,72,74 and the exposed area of layer 44to complete the finishing and protective coat on the lower surface ofthe floating cover.

Of course, although this embodiment shows test ports 91 and drain ports191 together, other embodiments may have one or more test ports 91without any drain ports 191 and yet further embodiments may have one ormore drain ports 191 without any test ports 91.

Further variations include providing a cover having a slight camberand/or rainwater drainage, which is particularly suitable for a tankwithout a roof. The cover need not be round and it may be square,rectangular, or of any shape for fitting into any storage tank orreservoir to function as a cover. Instead of forming the in-fillsandwich sections on site, these could be prefabricated at the factory.

While only one embodiment of a cover and method of its construction havebeen described and illustrated in detail, it is to be understood thatmany changes, modifications and variations could be made to the presentinvention without departing from the scope of the invention.

1. A generally planar buoyant panel for a floating cover for a liquidstorage tank, the panel comprising first and second portions in contactwith each other, and wherein: the first portion has an extent in theplane of the panel and a first side facing the second portion; thesecond portion has an extent in the plane of the panel, which extent isless than the extent of the first portion; and the first portion has anexposed portion on said first side.
 2. A panel according to claim 1,wherein the second portion has an edge and the exposed portion extendsall the way around the edge of the second portion.
 3. A panel accordingto claim 1, wherein the first portion is a laminate structure.
 4. Apanel according to claim 1, wherein the first portion is a glassreinforced structure.
 5. A panel according to claim 1, wherein thesecond portion is buoyant.
 6. A panel according to claim 1, for use withthe second portion being above the first portion.
 7. A panel accordingto claim 1, wherein the first and second portions are continuous.
 8. Apanel according to claim 1 further comprising a third portion in contactwith the second portion on the other side of the second portion from thefirst portion.
 9. A panel according to claim 8, wherein the thirdportion has a first side facing the second portion and an extent in theplane of the panel, which extent is the same as or less than that of thesecond portion.
 10. A panel according to claim 8, wherein the thirdportion has a laminate structure.
 11. A panel according to claim 10,wherein the layers of the third portion each have an extent in the planeof the panel and the extent of the layer of the third portionfurthermost away from the second portion is less than the extent of thelayer of the third portion nearest the second portion.
 12. A panelaccording to claim 8, wherein the third portion is a glass reinforcedstructure.
 13. A panel according to claim 8, wherein the third portionhas the same construction as the first portion.
 14. A panel according toclaim 1, wherein the panel is generally a parallelepiped in the plane ofthe panel.
 15. A plurality of panels, each as defined in according toclaim 1, wherein the first portion of each panel has an edge generallyorthogonal to the plane of the panel, and the edges of the firstportions of adjacent panels abut each other.
 16. A plurality of panelsaccording to claim 15, further comprising a plurality of infillportions, each infill portion extending in contact with the exposedportions of two adjacent and abutting panels.
 17. A plurality of panelsaccording to claim 16, wherein each infill portion comprises an infillfirst portion, an infill second portion and an infill third portion, theinfill second portion is sandwiched between the infill first portion andthe infill third portion, and the infill second portion has the sameconstruction as a panel second portion.
 18. A plurality of panelsaccording to claim 17, wherein each infill third portion has the sameconstruction as a panel first portion, inverted.
 19. A plurality ofpanels according to claim 17, wherein in each infill portion: the infillthird portion has an extent in the plane of the panels between theinfill portion extends and a first side facing the infill secondportion; the second portion has an extent in the plane of the panelsbetween which infill panel extends, which extent is less than the extentof the infill third portion; a the extent of the infill third portionnot covered by the infill second portion extends onto and in contactwith outer surfaces of the panels between which the infill panelextends.
 20. A plurality of panels according to claim 19, furthercomprising a third portion in contact with the second portion on theother side of the second portion from the first portion, wherein theextent of the infill third portion not covered by the infill secondportion extends onto and in contact with outer surfaces of the panelthird portions panels between which the infill panel extends.
 21. Aplurality of panels according to claim 20, further comprising a thirdportion in contact with the second portion on the other side of thesecond portion from the first portion, wherein the third portion has alaminate structure wherein, the layers of the third portion each have anextent in the plane of the panel and the extent of the layer of thethird portion furthermost away from the second portion is less than theextent of the layer of the third portion nearest the second portion,wherein the extent of the infill third portion not covered by the infillsecond portion is in contact with layers of the panel third portionsbetween which the infill extends, other than the layer of each of thosepanels furthermost away from the second portion.
 22. A plurality ofpanels according to claim 17, further comprising a third portion incontact with the second portion on the other side of the second portionfrom the first portion, wherein the third panel has a laminatestructure, wherein each infill first portion has the same constructionpanel third portion without the layer furthermost away from the panelsecond portion and inverted.
 23. A plurality of panels according toclaim 16, comprising: one or more drain ports extending from a boundarybetween said infill portions and one of said panel second portions. 24.A plurality of panels according to claim 23, wherein the first portionis a laminate structure, and, wherein said one or more drain portsextends from a first end thereof flush with an inner most laminate layerof said laminate structure.
 25. A plurality of panels according to claim15, wherein the panels are prefabricated before being laid and joinedtogether where they are to be used.
 26. A plurality of panels accordingto claim 16, further comprising: at least one testing port extendingfrom a boundary between the infill portion and one of the panel secondportions to an external surface of one of the panel third portions. 27.A buoyant cover for a liquid storage tank comprising a plurality ofpanels according to claim
 15. 28. A method of joining a plurality ofgenerally planar buoyant panels together, for use in forming a floatingcover, wherein each panel comprises first and second portions in contactwith each other, with the first portion of each panel having an extentin the plane of the panel and a first side facing the second portion,the second portion of each panel having an extent in the plane of thepanel, which extent is less than the extent of the first portion; andthe first portion having an exposed portion on said first side, andwherein the plurality of panels are placed together, with adjacentpanels abutting each other, the edges of the first portions of adjacentpanels which are orthogonal to the planes of the panels being incontact, the method comprising the step of: inserting infill portionsbetween adjacent panels, the infill portions extending in contact withthe exposed portions of adjacent and abutting panels.
 29. (canceled) 30.A method according to claim 28, wherein the plurality of panels areprefabricated off-site before being positioned for joining together. 31.A method according to claim 30, further comprising the step, precedingthe inserting step, of roughening exposed surfaces of said panels andcleaning away dust generated thereby.
 32. A method according to claim28, wherein the inserting step comprises: placing a first infill layerover the exposed portions of adjacent and abutting panels; and placingone or more further infill layers over the first infill layer, one at atime.
 33. A method according to claim 32, further comprising the step ofrolling each infill layer after placing it to remove air.
 34. A methodaccording to claim 32 or 33, wherein at least the first infill layer isa non-laminated layer.
 35. A method according to claim 28, wherein thepanels are securely joined together by people working on just one sideof the cover.
 36. A method according to claim 28 used to produce abuoyant cover for a liquid storage tank comprising a series of panels.37. A method according to claim 28 being a method of forming a floatingcover.
 38. A method of constructing a floating cover for a liquid tankfrom a plurality of panels, wherein the panels are securely joinedtogether by people working on just one side of the cover.
 39. A methodof constructing a floating cover for a liquid tank from a plurality ofpanels, comprising the steps of: placing said plurality of panels on aform work; joining said panels together; and removing said form work;wherein the joining step prior to the removing step is accomplishedsolely from one side of the cover.
 40. A method for testing theintegrity of joints in a floating cover formed by a plurality of panelsaccording to claim 1 and further comprising: a third portion in contactwith the second portion on the other side of the second portion from thefirst portion; a plurality of infill portions, each infill portionextending in contact with the exposed portions of two adjacent andabutting panels, wherein the first portion of each panel has an edgegenerally orthogonal to the plane of the panel, and the edges of thefirst portions of adjacent panels abut each other; the methodcomprising: providing at least one testing port extending from aboundary between the infill portion and one of the panel second portionsto the external surface of one of the panel third portions; applying apressure differential between the testing port or one of the testingports and the outside of the cover; determining if there is a leakbetween the one testing port or said one of the testing ports and theoutside of the cover; and if there is a leak, identifying the leak. 41.A method of testing according to claim 40, wherein applying a pressuredifferential comprises pumping a gas into the one testing port or saidone of the testing ports at a predetermined pressure.
 42. A method oftesting according to claim 41, wherein said gas is air or nitrogen. 43.A method according to claim 40, wherein applying a pressure differentialfurther comprises sealing said one testing port or said one of thetesting ports at a predetermined pressure.
 44. A method of testingaccording to claim 43, wherein determining if there is a leak comprisesdetecting if there is a change in pressure over time in said one testingport or said one of the testing ports.
 45. A method of testing accordingto claim 40, wherein identifying the leak comprises applying a liquid toportions of said floating cover and observing bubbles formed in theliquid due to a leak.
 46. A method of testing according to claim 45,wherein said liquid is a soap solution.
 47. A method of testingaccording to claim 40, further comprising providing a sleeve in said atleast one testing port to apply the pressure differential to said atleast one testing port.
 48. A method of testing according to claim 40,wherein there is a plurality of the testing ports and all but one issealed as the pressure differential is applied to that one.
 49. A methodof joining a plurality of generally planar buoyant panels together, foruse in forming a floating cover, wherein each panel is as defined inclaim 1, and wherein the plurality of panels are placed together, withadjacent panels abutting each other, the edges of the first portions ofadjacent panels which are orthogonal to the planes of the panels beingin contact, the method comprising the step of: inserting infill portionsbetween adjacent panels, the infill portions extending in contact withthe exposed portions of adjacent and abutting panels.